Various attempts have been made to determine the fertile and infertile periods in women by a variety of electrical measurements. U.S. Pat. No. 4,328,809 relates to a device for detecting the potential level of the electromagnetic field of a living organism, and purports to assess the time of ovulation by measuring the electrical potential difference between index finger, middle fingers and thumbs, the peak levels of potential being supposedly indicative of the occurrence of ovulation. A commercial device termed "Menstrual Cycle Monitor" measures ionic changes in saliva and cervical mucus by determining the changes of electrolyte content of these.
A device has been described which makes use of four electrodes, and this is set out in FIG. 1. This is not part of the present invention and was the first attempt by the inventor to measure changes in electrical resistance in the vaginal walls of a woman to determine ovulation. In the four-electrode technique, a high frequency current of the order of several tens of KHz of a known intensity (tens of .mu.A) is sent through the electrodes 1 to 4 into the vaginal wall. Electrodes 2 and 3 are connected to an amplifier which has a very high input resistance, of the order of hundreds of Meg-ohms Due to its high input resistance the amplifier measures the voltage V across the electrodes 2 and 3, without drawing practically any current, and therefore the impedance of the metal/tissue interface which is a function of the current flowing through it, and interferes with the tissue resistance measurement can be neglected. Thus, the measured voltage V equals .sup.I .times.R, where I is the known current and R is the resistance of the vaginal wall stretch between the electrodes 2 and 3. Thus R can be calculated as V/I.
FIG. 1 illustrates a four-electrode probe marketed by ZETEC , which is intended to detect the fertile period in the cycle of a woman. This is termed "VER" (Vaginal Electrical Resistance) Method. This seems to be based on an earlier development by the inventors of the present invention.
U.S. Pat. No. 4,753,247 purports to measure the same phenomena, but by means of another parameter--a minimum of admittance--which is measured by means of semiconductor electrodes. The frequencies used according to that U.S. Patent are lower by an order of magnitude, and according to FIGS. 9 and 10 the DC and AC currents are superpositioned. Furthermore, the results reported in the U.S. patent show that lowest admittance was measured on the 12th day of the cycle at 1 KHz frequency, and on the 17th day with a frequency of 10 KHz. According to the present invention the 16th day is pinpointed by the actual measurements. The 12th day and 17th day results are clearly not acceptable as they fail to indicate the critical period of ovulation The above is clearly evident from FIG. 5 of the said U.S. Patent.
According to the present invention the four-electrode probe and the above method of measurement has been abandoned, as the present invention provides simplified yet more accurate and reliable means for predicting the fertile and infertile phase in the cycle of a woman.